I. Field of the Invention
Embodiments of the present invention relate to broadband antenna, and more particularly, to low-profile cavity broadband antennas having an anisotropic traverse resonance condition.
II. Description of the Related Art
High index dielectric ceramics have been used to create low profile antennas at low UHF bands, for instance. However, these are generally bandwidth limited due to the fact that it is very difficult to match a high dielectric material over more than a narrow band. This stems from the fact that impedance is calculated as Zo=(μ/∈)^0.5 which becomes very small as ∈ increases.
Techniques using double negative (DNG) metamaterials which mimic a perfect magnetic conductor (PMC) ground plane using a principle known as electro-band gap (EBG) have been considered. Using antenna image theory, a PMC ground plane allows an antenna to approach the ground plane without cancelling out its radiation pattern, however, PMC ground planes do not exist naturally. DNG materials yield a negative μ and ∈, but again are very bandwidth limited. This is because currently metamaterials only exhibit these negative properties at a narrowband resonance. Therefore, theoretically a nearly infinitely thin antenna could be created using this technique, but not with wide bandwidth operational characteristics.
Thus, improvements to low-profile antennas would be useful.